In a uranium recovery process, the uranium ore is subjected to an extraction process wherein the minerals found in the ore are extracted by a leaching solution. The pregnant leachate is subjected to purification and concentration processes to be followed by a precipitation process wherein the mineral values are precipitated.
The association of uranium with other ore constituents such as vanadium, molybdenum, copper, and thorium may require that special purification processes be included in the process in order to avoid certain processing problems and to prevent contamination of the uranium product. As a result, these additional constituents may become sufficiently concentrated at some point in the process to justify further treatment and the subsequent production of valuable by-products. These by-products sometimes reach a value equal to or possibly greater than that of the uranium, and the process then is usually designed for parallel production of both commodities. This is the case, for example, with ores in the Uraven Mineral Belt which are high in vanadium content.
Several known processes for the treatment of ores containing uranium and vanadium are described in Merrit, R.C., The Extractive Metallurgy of Uranium, Colorado School of Mines Research Institute, 1971, pp. 422-542. These process apply to the above-ground operations in which the ores have to be brought up to the surface by mining. One such method utilizes strong acid leaching in two stages to improve the vanadium recovery. In the first stage a strong acid solution having a pH less than 1.8 is utilized to leach the uranium. The second stage utilizes a strong acid solution having a pH between 1.8 and 2.2 to leach the vanadium values therein.
Another process is to separate the ore so as to treat material containing uranium but with a relatively low vanadium content in a direct acid leaching step, while other ores higher in vanadium content are initially salt roasted. The roasted ores are water leached to remove soluble sodium vanadate, and the residue is then acid leached to dissolve the uranium.
Merritt describes another process for the recovery of uranium and vanadium from ores by initially subjecting the ores to a roasting and water leaching process to remove some of the vanadium. A carbonate leach process is followed to recover uranium and vanadium. Then the residue is further subjected to an acid leach process to recovery some more uranium and vanadium.
While the above processes have been successful to some extent for above ground operations, there is still a need for improved processes for recovering both uranium and vanadium from ores containing the same. Accordingly, the present invention provides a two-stage leaching process wherein the uranium and vanadium mixing is held to a minimum thus reducing the amount of solution subjected to separation steps. Furthermore, the present invention could be applied to either in-situ or surface leaching operations.